1. Field of the Invention
The present invention relates to an organic light emitting display and a driving method thereof.
2. Discussion of Related Art
Recently, among various display devices, organic light emitting display devices have been proposed as the next-generation emissive display devices. Such organic light emitting display devices emit light by an electric field applied across an organic light emitting diode of a pixel.
FIG. 1 is a cross-sectional view showing a pixel of a conventional organic light emitting display. FIG. 2 is an equivalent circuit diagram of the pixel shown in FIG. 1.
With reference to FIG. 1, the pixel 1 includes a metal electrode 101, a transparent electrode 102, an organic phosphorous layer 103, and an organic hole transport layer 104. The metal electrode 101 functions as a cathode, and the transparent electrode 102 functions as an anode. The organic phosphorous layer 103 and the organic hole transport layer 104 are laminated between the metal electrode 101 and the transparent electrode 102. The organic phosphorous layer 103 and the organic hole transport layer 104 are made of organic compounds.
A glass substrate 105 is located at an outer side of the transparent electrode 102. A voltage from a drive source 106 is applied between the metal electrode 101 and the transparent electrode 102. Energy is discharged by excitons generated by recombination of electrons and holes, which are respectively introduced from the metal electrode 101 and the transparent electrode 102. Accordingly, the pixel 1 can emit light to an exterior through the transparent electrode 102 and the glass substrate 105. Since the pixel 1 has a structure in which the organic phosphorous layer is laminated between the electrodes, an equivalent electric circuit diagram thereof has parasitic capacitances. In more detail, as shown in FIG. 2, the pixel 1 includes an illuminant (or a light emitting element) 107 and a parasitic capacitance 109, which are connected with each other in parallel.
FIG. 3 is a schematic view showing a conventional organic light emitting display. FIG. 4 is a timing diagram showing application of a drive current for driving the organic light emitting display shown in FIG. 3.
With reference to FIG. 3 and FIG. 4, the conventional organic light emitting display includes an organic light emitting display panel 2, a controller 21, a scan driver 6, and a data driver 5.
In the organic light emitting display panel 2, column lines D1, D2, . . . , Dm and row lines S1, S2, . . . , Sn cross each other at predetermined intervals. Pixels 1, namely, organic light emitting diodes, are formed at crossings of the column lines D1, D2, . . . , Dm and the row lines S1, S2, . . . , Sn.
The controller 21 processes externally inputted image signals SIM, and provides data control signals SDA and scan control signals SSC to the data driver 5 and the scan driver 6, respectively. Here, the data control signals SDA include data signals, and the scan control signals SSC include switching control signals to generate a scan signal. The data driver 5 is electrically connected to the column lines D1, D2, . . . , Dm. The data driver 5 generates and provides a drive current corresponding to the data signals from the controller 21 to the column lines D1, D2, . . . , Dm according to the data control signals SDA from the controller 21.
The scan driver 6 is electrically connected to the row lines S1, S2, . . . , Sn. The scan driver 6 sequentially provides a scan signal to the row lines S1, S2, . . . , Sn according to the switching control signals SSC from the controller 21.
As shown in FIG. 4, during a drive period Td of an organic light emitting diode in one pixel, a ground voltage switching element (see, for example, Mg1, in FIG. 3) is turned-on to apply a ground voltage to a row line. During time periods except for the drive period, a scan voltage switching element (see, for example, MS1 in FIG. 3) is turned-on to apply a scan voltage to the row line. As shown in FIG. 4, during the drive period Td, a drive current is applied to a column line corresponding to a pixel. That is, during a drive period Td of a first row line S1, drive currents I1, I2, . . . , Im are respectively applied to the column lines D1, D2, . . . , Dm and flow through the respective pixels 1. As shown in FIG. 4, because the pixel 1 is equivalently represented by the illuminant 107 and the parasitic capacitance 109 connected in parallel with each other (see, for example, FIG. 2), the drive currents I1, I2, . . . , Im are divided into first drive currents Ic1, Ic2, . . . , Icm and second drive currents Id1, Id2, . . . , Idm. The first drive currents Ic1, Ic2, . . . , Icm function to charge the respective parasitic capacitances 109, whereas the second drive currents Id1, Id2, . . . , Idm are supplied to the respective illuminants 107 after a charge of the corresponding parasitic capacitances 109. FIG. 4 shows drive currents I1, I2, I3, and I4, which are respectively applied to a first column line D1, a second column line D2, a third column line D3, and a fourth column line D4.
Japanese patent publication No. 1999-231834 discloses an organic light emitting display and a driving method thereof as described above.
However, in Japanese patent publication No. 1999-231834, since the data driver 5 should include a circuit to generate the drive currents I1, I2, . . . , Im respectively applied to the column lines D1, D2, . . . , Dm, a manufacturing cost is increased.